A wide scope of human diseases and medical conditions are amenable to treatment by electric pulses delivered to specific areas of internal bodily organs or cells. Conditions that have been treated in this fashion include cardiac diseases, disorders of the brain (neurological and psychiatric), conditions of the spinal cord and peripheral nerves, and muscular disorders, to mention just a few.
In conditions of heart disease, such as acute myocardial infarction (MI), for example, the heart may go into ventricular fibrillation (VF). VF is typically treated by a prompt delivery of direct-current (DC) electrical shock to the patient's chest, known as defibrillation. In less acute disease conditions, cardiac arrhythmias may occur that require application of a milder DC shock for cardioversion. For extended treatment of arrhythmias, an artificial pacemaker is commonly used to control the heart rate. For this purpose, a suitable electrode is typically inserted into the heart by means of a catheter passed through the patient's venous system.
External defibrillation devices are typically based on discharge of a high-voltage, high-energy pulse (360 Joules for VF) from a capacitor. The strong pulse is needed in order to overcome the electrical resistance of body tissues and provide a sufficient stimulus to the patient's heart. To deliver the DC shock, a skilled operator smears a conductive protective gel on two large paddles and places them properly on the patient's chest, one over the heart base, the second over the heart apex. The operator ensures that no one is touching the patient, and then presses a button on each paddle to discharge the pulse into patient's chest. The results are typically observed on a electrocardiograph (ECG). As the electrical energy is only crudely directed to the heart, this routine may have to be repeated several times before the normal heart rhythm is recovered. This procedure causes trauma to the patient and entails a risk of severe electric shock to the treating personnel.
Attempts have been made to deliver electrical currents directly to the human heart or other internal body organs without surgical invasion or external electrical contacts, by applying a varying magnetic field to the body. For example, U.S. Pat. No. 4,723,536, whose disclosure is incorporated herein by reference, describes a device for heart pacemaking and pain reduction using external magnetic fields. An electromagnet comprising a wire coil is applied to the patient's body adjacent to the heart (for pacemaking) or to the head (for pain reduction). An alternating electrical current is applied to the coil in order to generate the desired magnetic field. The inventors indicate that the magnetic field intensity at the poles of the electromagnet that is needed in order to pace a human heart is 0.5 to 2.0 Gauss.
U.S. Pat. No. 5,170,784, whose disclosure is also incorporated herein by reference, describes a magnetic cardiac pacemaker using biphasic pulses of mixed frequencies and waveforms that are applied to a field coil, in order to generate magnetic pulses of relatively low intensity (less than 200 Gauss) without the use of leads. The device can be worn externally on the chest near the heart to enable the magnetic field to penetrate the body and control the heart muscle as a non-invasive cardiac pacemaker, or it can be inserted subcutaneously for long-term pacing.
U.S. Pat. No. 4,056,097, whose disclosure is likewise incorporated herein by reference, describes a contactless electromagnetic stimulus transducer, made of two curved ferromagnetic pole pieces with electric coils wound thereon. The pole pieces are designed to encircle (at least partially) the chest or the head of the patient, and are hinged in order to allow the distance between them to be adjusted. The electric coils are connected in opposition, so that the pole pieces generate opposing magnetic fields in the patient's body.